My 340 has an 8 vane water pump-6 vane water pumps for the 340 are readily available- 8 vanes are not & have to be sent off for rebuild-is the 8 vane needed for an essentially stock 71 Demon-340 or will the 6 vane be adequate for a street car with an occasional strip pass ? TIA

An 8 vane will flow more but a 6 vane will work & I'd weld a round anticav plate to the vanes, simple to do & vastly increases it's effectiveness

..the size of the pulley will determine the pump speed.
a small pulley will use the 8 and a large pulley will use the six
..or have i got that backwards?..the slow speed would use the 8.

8 is slower, non-ac car
6 vane is faster a/c car

they felt the 8 vane would cavitate more.

Thanks for the replies--guess I'll have the 8 vane rebuilt since it is a non-ac car

8 vanes = non A/C pullys-turns slower and pumps x amount of water at idle.

6 vanes = A/C pullys- turns faster and pumps same x amount of water at idle.

at higher RPM with the 8 vanes/smaller A/C pullys there is a chance it will cavitate.

the t-stat by-pass hose should not be blocked, it keeps the vanes from cavitating while t-stat is closed. you can block it if you run a restrictor plate instead of the t-stat.

welding a anti-cavitation plate onto the vanes helps flow and prevents cavatation.

is this the early cast iron WP?

I get a new, heavy duty cooling 5/8 shaft/large bearing 8 vane pumps at napa for 65$ (neck has ribs not gun barrels)

with all that said I have mixed match vane count and pully size many time and never had any trouble as long as the rest of cooling system was up to specs.

put a 6 vane on and run it.

A/C used the smaller pulley/6 vane so the fan would turn faster for more airflow at idle for additional cooling yet the 6 vane would keep it from cavitating at higher RPM's with the higher vane speed from the smaller pulley since the 6 vane flowed less coolant. For the whole scoup from the Master go to www.moparchat.com then scroll down to & click on "circle track chat" then read thru Sanborns' cooling mods that are in a sticky at the top of the page

Strongly urge the use of a 8 blade pump My 340 nalways ran hotter with a 6 blade pump I use a 6 blade on a 360 but I have a cavitation plate on it

Thanks for all the input guys- I've learned alot about water pumps- I've located a new heavy duty 8 vane at NAPA and will go with that--thanks again